Photoresist stripping compositions

ABSTRACT

A non-aqueous negative photoresist stripping composition which consists essentially of about 40 to 80% by weight of an alkylnaphthalene solvent, about 5 to 20% by weight of an alkyl phenol which provides a corrosion inhibitory effect, about 5 to 20% by weight of a linear monoalkylbenzene sulfonic acid which is a surfactant and about 1 to 10% by weight of a dialkylbenzene sulfonic acid. There is further provided a process for removing coatings from a photoresist with the compositions of the invention.

FIELD OF THE INVENTION

This invention relates to photoresist stripping compositions. Moreparticularly, the invention relates to a non-aqueous chlorine-freenegative photoresist stripping composition containing aromatic solventsand a mixture of aromatic sulfonic acids that can be easily rinsed awaywith water. Moreover, the composition is provided with a corrosioninhibitor.

BACKGROUND OF THE INVENTION

During manufacture of semiconductors and semiconductor microcircuits, itis frequently necessary to coat the materials from which thesemiconductors and microcircuits are manufactured with a polymericorganic substance, generally referred to as a photoresist, e.g., asubstance which forms an etch resist upon exposure to light. Thesephotoresists are used to protect selected areas of the surface of thesubstrate, e.g. silicon, SiO₂ or while such etchant selectively attacksthe unprotected area of the substrate. Following completion of theetching operation and washing away of the residual etchant, it isnecessary that the resist be removed from the protective surface topermit essential finishing operations.

It is necessary in a photolithographic process that the photoresistmaterial, following pattern delineation, be evenly and completelyremoved from all unexposed areas, in the case of positive resists, orexposed areas in the case of negative resists, so as to permit furtherlithographic operations. Even the partial remains of a resist in an areato be further patterned is undesirable. Also, undesired resist residuesbetween patterned lines can have deleterious effects on subsequentprocesses, such as metallization, or cause undesirable surface statesand charges.

A common method used in removing the photoresist from the substrate isby contacting the substract with an organic stripper. Heretofore theseorganic strippers have been composed of various components whose purposeit was to lift and remove the polymeric photoresist from the substrate.However, these stripping solutions have heretofore usually containedchlorinated hydrocarbon compounds which resulted in a distinctdisadvantage due to the toxicity as well as pollution problems arisingfrom their disposal.

Chlorinated hydrocarbons-free strippers are described in U.S. Pat. No.4,070,203 (issued Jan. 24, 1978 to Neisus et al). These strippers,having only an alkylbenzenesulfonic acid component of 12-20 carbons anda chlorine-free, aromatic hydrocarbon component with a boiling pointabout 150° C., suffer from the disadvantage that they cannot be easilyrinsed off the inorganic substrate after stripping with temperaturesthat are generally required for conventional stripping compositions.Moreover, such compositions are corrosive to many conventionalphotoresists.

It is highly desirable that stripping compositions be provided that areeffective and efficient stripping compositions for removal of coatingsfrom substrates that heretofore have resisted ready removal withconventionally available strippers.

It is also desirable that effective stripping compositions be providedthat are devoid of undesirable chlorinated components and which do notrequire the use of hot caustic components. Highly desirable arestripping compositions and use thereof that are not consideredundesirable by regulatory agencies overseeing their production and use.

U.S. Pat. No. 4,165,294 to John E. Vander Mey discloses a strippingsolution free from chlorinated hydrocarbons comprising a surfactant, analkylarylsulfonic acid and an aromatic hydrocarbon having a boilingpoint above 150° C. The aromatic hydrocarbons are optional and arepreferably mixtures of aromatic solvents having 9-13 alkyl carbons anddo not comprise more than 40 weight percent. The composition doeshowever cause pitting in many photoresist substrates.

U.S. Pat. Nos. 4,426,311; 4,395,348; 4,304,681; 4,221,674; 4,215,005 and4,165,295 each disclose the use of an organic sulfonic acid in aphotoresist stripping composition. However, the organic sulfonic acid isutilized in combination with solvents having the aforementioneddisadvantages.

U.S. Pat. No. 4,992,108 to Ward et al, which is herein incorporated byreference, discloses non-aqueous biodegradable negative photoresiststripping compositions which contain an aromatic solvent and an organicsulfonic acid. The present invention provides a specific improvementover the formulations disclosed therein. The compositions in this patentcannot be used on some conventional photoresist substrates for prolongedperiods because of their corrosive effects.

It is an object of the invention to provide a non-aqueous negativephotoresist stripping composition which can be used at a wide range ofoperating conditions and at lower temperatures without corrosion of thephotoresist substrate.

It is another object of this invention to provide a photoresiststripping solution which is essentially free of naphthalene andchlorinated hydrocarbon compounds.

It is an additional object of this invention to provide such a solutionwhich is substantially clean water rinseable such that the hydrocarbonsolvent does not oil out and the polymer does not reprecipitate duringrinsing.

SUMMARY OF THE INVENTION

The present invention relates to a non-aqueous negative photoresiststripping composition consisting essentially of an alkyl phenol, analkylnaphthalene solvent, a surfactant consisting of a linearmonoalkylbenzenesulfonic acid and a dialkyl sulfonic acid. Moreparticularly, the stripping composition consists essentially of about5-20% by weight of composition of an alkyl phenol, about 5-20% by weightof composition of a surfactant comprising a linearmonalkylbenzenesulfonic acid about 1-10% by weight of composition of adialkylbenzene sulfonic acid and about 40-80% by weight of compositionof a mono-or dialkyl naphthalene wherein the alkyl group contains 1-4carbon atoms.

The invention also relates to a method for removing a coating from asubstrate utilizing the composition of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a composition which is effective inremoving negative photoresists from an inorganic substrate, has a lowtoxicity and could be used over a wide temperature range and at lowtemperatures. While organic sulfonic acid have been previously used instripping compositions, they have been used in combination with solventsthat presented problems in disposal and use.

It has been surprisingly discovered that when a surfactant linearmonalkylbenzenesulfonic acid is used in combination with an alkyl phenolwhich acts as an inhibitor and a surfactant, such as nonyl phenol, andanother sulfonic acid, namely dialkylbenzene sulfonic acid, togetherwith a solvent essentially comprising a mono- or dialkyl naphthalene,there is provided a composition which results in a surprisingimprovement in removing coatings from negative photoresists, whichcoatings will not redeposit, is cleanly rinseable with water and doesnot cause corrosion.

The photoresist stripping composition of the invention essentiallyconsists of about 5-20% by weight of a surfactant consisting essentiallyof a linear monoalkylbenzene sulfonic acid, about 1-10% by weight ofdialkylbenzene sulfonic acid, about 5-20% of an alkyl phenol and about40-80% by weight of a solvent comprising a mono--or dialkyl naphthalenewherein the alkyl group contains 1-4 carbon atoms.

A preferred composition of the invention consists of about 60-75% byweight of a mixture of mono--and dimethylnaphthalenes, about 8-15% byweight of nonylphenol, about 12-18% by weight of dodecylbenzene sulfonicacid and about 3-6% by weight of xylenesulfonic acid.

The solvents which can be utilized in the present invention are thealkyl naphthalenes of the formula: ##STR1## wherein X is an alkyl groupof 1 to 6 carbon atoms, and X¹ is selected from the group consisting ofhydrogen and alkyl of 1 to 6 carbon atoms.

Suitable alkyl naphthalenes include monomethylnaphthalene,dimethylnaphthalene (for example 1,3-dimethylnaphthalene,1,4-dimethylnaphthalene), diethylnaphthalene, methyl, ethylnaphthaleneand mixtures thereof.

The alkyl phenols which can be used in the present invention and whichprovide a corrosion inhibiting effect are of the general formula:##STR2## wherein R₁, R₂ and R₃ are each selected from the groupconsisting of hydrogen and an alkyl group of 1-9 carbon atoms with theproviso that at least one of R₁, R₂ and R₃ is alkyl.

Suitable alkyl phenols which may be utilized in the invention includet-butyl phenol, octyl phenol, nonyl phenol, 2,4-dimethyl phenol,2,4-diethyl phenol, and the like. Preferable are the alkyl phenols whichnot only provide a corrosion inhibitory effect but are surfactants, suchas nonyl phenol.

Suitable surfactant type linear alkylbenzene sulfonic acids which may beused include linear octyl-, decyl- and dodecylbenzenesulfonic acid.

Suitable dialkylbenzenesulfonic acids are those containing two alkylgroups each, preferably linear, and composed of 1 to 4 carbon atoms andinclude the isomers of xylenesulfonic acid and the isomers ofmethylethylbenzene sulfonic acid. Preferred are the isomers ofxylenesulfonic acid either individually or in admixture.

The polymeric organic substances which are to be removed by thestripping solutions of the invention are photoresists which generallycomprise polymers selected from relatively low molecular weightpolyisoprenes, polyvinyl cinnamates and phenol formaldehyde resins.These photoresists are applied to a substrate, e.g., SiO₂, silicon oraluminum and portions are masked. The masked substrate is then exposedto light, e.g., a 120 volt 650 watt quartz lamp for 1-15 seconds at adistance of 6-12 inches to harden the exposed photoresist. The portionof the photoresist which is not exposed is removed by solventdevelopment, thus leaving a pattern, e.g., a portion of an electricalcircuit pattern, on the exposed substrate. The remaining photoresist isthen baked for further hardening and the portion of the substrate whichis not covered by the photoresist is etched or otherwise treated. Theetchant may be a buffered oxide, acid or plasma etchant which mayfurther harden the photoresist. The hardened photoresist must then beremoved before the substrate can be further processed or used. Inemploying the stripping solutions of this invention, the substratecovered with the baked photoresist is contacted with the strippingsolution at a temperature of from about 25° C. to about 95° C.,preferably between 50° and 70° C. The period required for stripping thephotoresist vary to quite an extent, depending on the specific polymerused in the photoresist and photoresist processing conditions.Generally, the time involved will be between 1 and 10 minutes, althoughsome resists, depending upon the bake temperature, may require 15minutes, 30 minutes or longer before the polymeric photoresist isloosened from the substrate. It should be appreciated that manyphotoresists are completely dissolved off the substrate while others maybe loosened, then floated off, and then dissolved in the strippingcomposition.

After the photoresist has been stripped from the substrate, thesubstrate is rinsed in any aqueous rinsing liquid. A solvent rinse mayfollow the stripping step, with solvents such as isopropanol,butylcellosolve or methylcellosolve being used. Since, however, thepresent compositions are substantially and cleanly water rinseable, itis acceptable to rinse with deionized water of the purity commonly foundin semiconductor processing directly after stripping.

The stripping compositions of this invention are effective in strippinga wide and varied range of paints, enamels, lacquers, varnish, urethanecoatings, powder and photoresist coatings and the like from varioussubstrates such as wood or metal. As examples of wood or metal coatingsthat are stripped with the stripping compositions of this inventionthere may be mentioned, for examples, the following type coatings:linseed oil modified polyurethanes, white shellac, nitrocellulosecoconut oil alkyds, acrylic modified alkyds, vinylacetate/styrene/acrylic resins, tall oil-soya alkyds, soya-tung oilpolyurethanes, tall oil linseed alkyds, epoxy paint, modifiedepoxy-ester resin paints, oil based enamels, alkyd enamels, marinevarnishes, marine semi-gloss oil bases, latex enamels, lacquers,vinyl/acrylic resins, acrylic latexes, acrylic resins, phenolic resinsand novolac/resole resins. The stripping compositions are alsoespecially useful for stripping multiple layers of auto, airplane andmetal enamels from metal substrates and are able to do so in a shortertime period and at a lower temperature than those previously used incommercial stripping compositions and methods.

The stripping compositions of this invention are especially useful andadvantageous for numerous reasons among which may be mentioned thefollowing. The stripping compositions are water rinseable,non-corrosive, and of low toxicity to humans and the environment. Thestripping compositions may be recycled for multiple use or easilydisposed of in an environmentally safe manner without the necessity forburdensome safety precautions. The stripping compositions of thisinvention evidence higher stripping efficiency at lower temperatures fora wide variety of coatings and substrates. Moreover, the strippingcompositions are easily prepared by simply mixing the components at roomtemperature and thus require no special human or environmental safetyprecautions. Furthermore, the components of the stripping compositionsof this invention provide synergistic stripping action and permitreadily and substantially complete removal of coatings from substrates.

The effectiveness and unexpected nature of the stripping compositions ofthis invention is illustrated, but not limited, by the data presented inthe following example.

EXAMPLE 1

A single coat of semi-gloss oil based enamel (white) from Cook and DunnPaint Corporation, Newark, N.J., was brushed onto test sample of birchwood at a temperature of about 21°-25° C. and permitted to cure/dry fora period of four weeks at this temperature. The wood test sample allevidenced good water absorption properties prior to painting. Followingthe cure/dry steps, the test samples were subjected to stripping bybrushing equivalent amounts of various stripping compositions on thepainted substrates and resting the samples set for a specified period oftime without disturbance. A soft cloth rag was then wetted with thestripping compositions and an attempt at finish removal was made byrubbing the test sample with the wetted rag.

Stripping compositions consisting solely of m-diisopropylebenezene ordodecylbenzene sulfonic acid, individually, each removed less than 50%of semi-gloss oil based enamel coating following a residence time ofstripping compositions on the painted test samples of at least 8minutes. In contradistinction, a stripping composition of thisinvention, consisting of 70% by weight of aromatic 200 N.D. (anaphthalene depleted solvent consisting of a mixture of mono- anddimethylnaphthalenes), 16% by weight of dodecylbenzenesulfonic acid, 4%by weight of xylenesulfonic acid and 10% by weight of nonylphenolremoved 100% of the semi-gloss oil based enamel coating after aresidence time of 5 minutes.

EXAMPLE 2

In order to demonstrate the efficiency of the different solventcompositions as negative photoresist strippers, the following tests wereperformed.

Metal substrates containing commercial negative photoresists werepost-baked. The substrates were cooled and dipped into a vesselcontaining a stripping composition of the present invention maintainedat 65° C. and stirred with a magnetic stirrer. The substrate was removedand dipped into a vessel containing isopropyl alcohol maintained at roomtemperature for 1 minute and then rinsed with deionized water.

The results were as follows:

    ______________________________________                                                                           Stripping                                  Test Stripping   Negative  Post Bake/                                                                            Results;                                   No.  Compositions %                                                                            Photoresist                                                                             60 min. °C.                                                                    % wafer cleared                            ______________________________________                                        A    nonyl phenol                                                                              KTI-747*  none     0                                              aromatic 200 ND                                                                           SC-100**  none     0                                              (25/75)     KTI-747   150      0                                                          SC-100    150      0                                         B    dodecylbenzene                                                                            KTI-747   none    <50%                                            sulfonic acid                                                                             SC-100    none    <50%                                                        KTI-747   150     <50%                                                        SC-100    150     <50%                                       C    dodecylbenzene                                                                            KTI-747   none    100%                                            sulfonic    SC-100    none    100%                                            acid 16%,   KTI-747   150     100%                                            xylene sulfonic                                                                           SC-100    150     100%                                            acid 4%,                                                                      nonyl phenol 10%                                                              aromatic,                                                                     200 ND 70%                                                               ______________________________________                                         *Polyisoprene type negative resist from Eastman Kodak Co.                     **negative resist from OlinHunt                                          

EXAMPLE 3

The operating parameters of various stripping compositions were obtainedeither from product literature or independent test with the followingresults:

    ______________________________________                                        Sample I                                                                             m-Diisopropylbenzene      75%                                                 Dodecylbenzene sulfonic acid                                                                            25%                                          Sample II                                                                            Composition sold by Indust-Ri-Chem Laboratory                                                           50%                                                 Inc. under the trade name J-100                                               Chlorinated aliphatic and                                                     aromatic hydrocarbons                                                         Phenol                    10%                                                 Benzene sulfonic acid     40%                                          Sample III                                                                           Composition sold by EKC Technology Inc. under                                                           <75                                                 the trade name Burmar Nophenol 922                                            C.sub.9 -C.sub.12 Paraffins, cycloparafins,                                   aromatics                                                                     Catechol                  <5                                                  Dodecylbenzensulfonic acid                                                                              <40                                          Sample IV                                                                            Composition of the invention                                                                            70%                                                 aromatic 200 ND                                                               Nonyl phenol              10%                                                 Dodecylbenzene sulfonic acid                                                                            16%                                                 Xylene sulfonic acid      4%                                           ______________________________________                                        Sample    I        II         III     IV                                      ______________________________________                                        Resist    Neg      Pos-Neg    Pos-Neg Neg                                     Type                                                                          Recommended                                                                             25-85    90-100     95-105  25-95                                   Operating Temp                                                                (°C.)                                                                  Composition                                                                             Stable   Rapid      Rapid   Stable                                  Stability on       Change     Change                                          Heating                                                                       Water     Cleanly  Not        Rinseable                                                                             Cleanly                                 Rinseability                                                                            Rinseable                                                                              Recommended                                                                              High    Rinseable                               Toxicity  Low      High       Degrades                                                                              Low                                     Performance                                                                             Stable   Degrades           Stable                                  Change on                                                                     Prolonged                                                                     Heating                                                                       Reactivity to                                                                           25 A/min 20 A/min   25-30 A/min                                                                           0-5 A/min                               Metals    (80° C.)                                                                        (100° C.)                                                                         (95°)                                                                          (80° C.)                         (Al Etch  (Strip)  (Strip)    (Strip) (Strip)                                 Rates)                                                                        ______________________________________                                    

While the use of the hereinbefore recited stripping compositions of thisinvention has been described in connection with certain specificcoatings and substrates for purposes of illustration, it will beappreciated that the stripping compositions of this invention aresuitable for other stripping uses which will be apparent to thoseskilled in the art and can be employed with a variety of coatings on avariety of substrates in a variety of environments and industries.

What is claimed is:
 1. A non-aqueous naphthalene-free negativephotoresist stripping composition consisting essentially of about 40 to80% by weight of an aromatic hydrocarbon solvent of the formula:##STR3## wherein X and X₁ are the same or different and each is a memberselected from the group consisting of hydrogen and an alkyl group of 1to 4 carbon atoms with at least one of X and X¹ being alkyl;about 5 to20% by weight of a surfactant consisting essentially of a linearmonoalkylbenzene sulfonic acid; about 1 to 10% by weight of adialkylbenzenesulfonic acid wherein said alkyl groups contain 1 to 4carbon atoms, and about 5 to 20% by weight of an alkyl phenol of thegeneral formula: ##STR4## wherein R₁, R₂, and R₃ are each selected fromthe group consisting of hydrogen and an alkyl group of 1 to 9 carbonatoms wherein at least one of R₁, R₂ and R₃ is alkyl, and whereby saidalkyl phenol provides a corrosion inhibitory effect.
 2. The strippingcomposition of claim 1 wherein said surfactant is dodecylbenzenesulfonic acid.
 3. The stripping composition of claim 1 wherein saidalkyl phenol is nonyl phenol.
 4. The stripping composition of claim 1wherein said solvent is selected from the group consisting ofmethylnaphthalene, dimethylnaphthalene and mixtures thereof.
 5. Anon-aqueous naphthalene-free photoresist stripping compositionconsisting essentially of about 60 to 75% by weight of a solventconsisting of methylnaphthalene, dimethylnaphthalene and mixturesthereof, about 8 to 15% by weight of nonylphenol, about 12 to 18% byweight of dodecylbenzene sulfonic acid and about 3 to 6% by weight ofxylenesulfonic acid.